written by Dr YP Tai
(Last updated on Oct 15th 2020)
What is colonoscopy?
A colonoscopy is an examination of the inside lining of the large bowel. A flexible tube, about the thickness of a finger, is inserted into the anus and slowly passed up the large
bowel. Any abnormalities will be visualized on the monitor screen. Polyps are usually removed at the same time if they are small. For large polyps, tumours or inflammation,
biopsies will be taken for further evaluation. taken for further evaluation.
Why is colonoscopy done?
Colonoscopy is indicated if an abnormality of the large bowel is suspected or to be excluded. This might be done for people with symptoms like bleeding from the back
passage, persistent abdominal pain, change in bowel habits, unusual diarrhea, abnormality from CT scan, previous history of colonic polyps, or family history of colonic cancers.
It has been recommended that even healthy people should undergo colonoscopy at age of 50, and every 10 years thereafter, to exclude presence of colonic polyps and to have
these removed before they become cancerous.
What preparations are required for colonoscopy?
In order to examine the inside lining of the large bowel clearly, the large bowel must be cleansed properly. This can be achieved in a variety of ways, depending on the
preference of the doctor. In general, a special laxative in form of tablets or solution is taken by mouth the day before the examination. It is usually repeated 10-12 hours later
to ensure complete cleaning of the large bowel. Diarrhoea usually occurs 1-2 hours after taking the laxative. Passing clear fluids or mucus would indicate good cleansing of the
bowel. Bowel preparation will be helped if a low fibre diet is taken three days before the examination.
What happens during colonoscopy?
You will be transferred to the Endoscopy Room. An intravenous cannula will be inserted into the back of your hand, if it is not already done. A cuff is put around your arm to
monitor the blood pressure and a clip on one of the fingers to monitor the oxygen level. You will be asked to lie on the left side. Medications will be given intravenously to
make you sleepy and reduce discomfort. The drugs are either given by the endoscopist or by the nurse on the doctor’s instruction. In some cases, the medication is given by
an anaesthetist. The doctor will now insert the colonoscope into your anus and slowly advance it up your colon. At this stage, you might feel some bloating of the abdomen and
maybe some pressure or discomfort. The examination normally takes 15 to 45 minutes depending on the nature of the colon and what additional procedures are required. In
some cases, the examination might not be completed due to looping of the bowel or poor bowel preparation. In that case, your doctor might arrange repeat examination on
another day or an alternative form of examination.
What happens after colonoscopy?
Immediately after colonoscopy you will be put into an observation area to recover. You will probably sleep for a while from the sedation. Normally you will be allowed home
about two hours after the procedure. You should not drive after the procedure, and it is a good idea to have somebody to pick you up and accompany you home. Your doctor will
arrange follow up appointment for you especially when biopsies or removal of polyps (polypectomy) have been done.
What are the possible complications of colonoscopy?
Colonoscopy is generally a safe procedure and complications are uncommon if done by a properly trained and experienced doctor. The most feared complication is
perforation of the colon, occurring in 0.05 to 0.1% of cases. It happens more commonly after polypectomy, in cases where the colon is twisted or stuck by adhesions (previous
abdominal operation), and in elderly people when their bowel wall is thin. If perforation unfortunately does occur, an operation under general anaesthesia will be required to
rectify the problem.
Bleeding can happen after polypectomy and after biopsy has been performed. The bleeding is usually minor and will stop by itself. Occasionally it requires control by
colonoscopy. After discharge if you develop severe abdominal pain, fever or passing fresh blood or blood clots, you must seek medical attention as soon as possible.